Short answer: the game has evolved quite a bit (I've been playing for 17 years).
Long answer:
> Anybody using the old ones is a sucker.
There are several different Constructed formats, each with its own restrictions on which cards can be played. The three most popular are Legacy, Modern, and Standard. In Modern and Standard, only newer cards are allowed, so there naturally aren't any from older sets. In Legacy, there are plenty of older cards being played. Take a look at the lists from any Legacy tournament, and you'll see a mix of old and new. Now, the power levels of each type of card have changed (in general, creatures have gotten more powerful and non-creature spells less powerful), so you'll often see earlier non-creature spells and more recent creatures, but this isn't set in stone.
There's also the idea of power creep. The natural progression of a game like Magic is to allow more and more powerful effects, since not doing so will dis-incentivize buying new cards. For at least the past 10 years, then, Wizards has made a conscious decision to vary the power level between blocks (cycles of sets). Different types of cards will be more or less powerful at different times (in the last block, enchantments were the focus, now multicolor cards are being emphasized).
It's true that if you want to stay competitive takes a certain amount of money, but this is true in many hobbies. Magic has been constantly getting more popular over the last few years, and it's still around when 99% of its competitors are gone. Let's check back on your game in 20 years and see where it's at.